Fossil fuels currently power the majority of modern internal combustion engines (ICEs). But hydro carbon fuels derived from petroleum and other stocks are a scarce resource and the extensive use of such fuels in automobiles is believed by many persons to contribute to undesirable climate change due to the byproducts of combustion. Therefore, there is tremendous pressure to increase the efficiency of the modern internal combustion engine. The demand for increased efficiency is also driven by government quotas, mandates and taxes regarding fuel consumption and CO2 emissions. And this is occurring simultaneously with increasing demands to enhance safety of automobiles, which often increases weight to the detriment of efficiency.
Current steps employed to increase efficiency of ICEs can add considerable cost and complexity while decreasing reliability, power and drivability. For example, there have been numerous attempts to add adjustability to the operation of the intake and/or exhaust valves during the operating cycles of ICEs.
Traditionally the intake and exhaust valves (also referred to as poppet valves) of an ICE have been actuated by one or more camshafts which are mechanically driven from the ICE crankshaft at half engine speed, thereby operating the valves in synchronism with the ICE rotation, and in a fixed phase with one another. It is also known to substitute rotary valves for poppet valves, again mechanically driving the valves from the crankshaft and rigidly slaving the valve operation to ICE crankshaft rotation.
The camshaft profile defines timing of the valve open/close movements. Camshaft design is an exercise in tradeoffs because a given camshaft profile can only be optimized for a very narrow range of crankshaft speeds (measured in rotations per minute (RPMs)). Thus compromises must be made to facilitate easy starting and operation over a broad range of speeds, and these compromises decrease the overall efficiency of the ICE and require great complexity.
Moreover, the mechanical camshaft has a fixed amount of valve movement (lift) and time that the valve is open (degrees of duration). The opening times and closing times of the valves are also rigidly fixed by the mechanical drive systems and camshaft profile. Adding additional camshafts and valves allows optimizing one camshaft/valve system for low speed and the other for high speed, but this still has to be compromised in order to allow easy starting and a broad range of operating speeds.
It is further known that the camshaft(s) may be rotationally advanced and/or retarded with respect to the crankshaft rotational position by various means such as hydraulically bi-directionally rotating the drive mechanism of the camshaft. This is referred to as “phasing” the cam. Phasing facilitates operation of the ICE at various times, temperatures, conditions, loads and altitudes. As is also well known, this form of making adjustments to engine timing may be enhanced further by adjusting valve lift in a variety of ways. However, such systems suffer from heightened complexity. For example, the manufacturing precision required of all of the many parts is heightened, which adds cost and points of failure.
Also, the precise viscosity of the hydraulic fluid required to operate the many parts further adds to costs and expense of maintenance. It is desirable to have the valve actuation systems use engine oil as the required hydraulic fluid for operation. But, even oils meeting current API and SAE specifications may not be precise enough viscosity to meet the requirements of these applications. This necessitates specialized lubricants be used, which limits the motorist's ability to acquire top-up oil, perform their own oil changes, and adds to the cost of automobile maintenance.
Further problems with the camshaft phasing technologies described above are that valve timing, valve duration and valve lift are fixed. These parameters can only be changed slightly and such change requires expensive and complex technology.
Certain attempts have been made to overcome the shortcomings of the technologies discussed above and achieve independent valve operating times and duration. For example, U.S. Pat. No. 4,009,695 discloses a Programmed Valve System for Internal Combustion Engine. This patent teaches a means for valve operation independent of crankshaft position, but suffers from problems inherent to hydraulic operation of the valves. In particular, operation of the valves involves cycling the valve from open to closed in an uncontrolled manner. Such operation is particularly damaging to the valve and valve seat upon the valve closing. Also, the length of stroke of the hydraulic movement (i.e., valve lift) is not variable in this mechanism.
U.S. Pat. No. 6,736,092 discloses an internal-combustion engine equipped with an electronically controlled hydraulic system for variable actuation of the inlet and/or exhaust valves of the engine. In particular, this patent teaches the use of a standard camshaft that is mechanically slaved to the crankshaft of an ICE, but with the additional disposition of an electronically controlled hydraulic lifter between the camshaft and the valve. Through electronic control of the hydraulic fluid in and out of the lifter, the opening and closing time of the valve and the lift of the valve can be controlled to some extent. However, this arrangement is limited to the operation of the mechanically slaved camshaft and, for instance, cannot command a valve to open at maximum lift for a long duration, or at a different time than the camshaft scheduled opening time.
Attempts have been made to make ICE valve operation independent of crankshaft positioning by driving the valves open and shut with hydraulic pressure that is applied by electrical means. An electrical command is sent by control unit, which receives input from engine and associated system sensors. However, such systems still suffer from significant drawbacks as will be explained below.
U.S. Pat. No. 5,572,961 discloses a Balancing Valve Motion in an ElectroHydraulic Camless Valvetrain. This patent teaches a minimization of hydraulic valve controls for the ICE valves and operation of an ICE using hydraulically operated ICE valves. High hydraulic pressure is used to push the valve in one direction while low hydraulic pressure combined with a balancing spring to cushion and stop the ICE valve movement. The multiple hydraulic valve controls per ICE valve, balancing springs and multiple hydraulic pressures add significant complexity to the system however. Further, it is difficult to control the ICE valve lift variations with this system.
U.S. Pat. No. 6,729,279 discloses an Apparatus for Controlling at Least One Engine Valve in a Combustion Engine. This patent teaches hydraulically operated valves in the ICE as controlled by a control system. It is taught that an upper chamber should be charged with fluid to close the ICE valve and a lower chamber should be charged to lift the valve. One drawback with this mode of moving an ICE valve is that the hydraulic fluid control valves can only be in open or closed states. The patent teaches that a “throttle” valve may be disposed in the hydraulic line to adjust the total movement (lift) and movement speed of the ICE valve, as the ICE valve moves from open to closed and vice versa. This patent also addresses the need for dampening of hydraulically operated ICE valves by utilizing a complex means to attempt to achieve such dampening.
It has also been attempted to operate the ICE valves by pneumatic means. Again, such configurations can actuate the valves independent of the ICE crankshaft position. For example, in U.S. Patent Application Publication No. 2013/0098337 A1, a so-called Free Valve System is disclosed. This system uses air directed through electrically operated control valves to push the ICE valves open and shut. A major drawback of such systems is that the ICE valves slam into their limit stops upon opening and also slam into the valve seats upon closing. Such slamming causes mechanical damage to the valves fairly quickly.
Yet another attempt to resolve the deficiencies of camshaft-operated valves has been to electrically operate the valves using computer control in a similar fashion to electronic fuel injection. To date, all of these include some form of solenoid for valve actuation and also a dampening means. A solenoid operates by fully opening and fully closing the device that it acts upon. Solenoids cannot be controlled to move at a variable rate or to vary speed upon opening/closing. The only way to vary the rate of opening, stopping, closing or movement distance (lift) in a solenoid operated system is with external mechanical devices, which add to the overall complexity of the system. The solenoid arrangement and drawbacks can be understood with reference to examples thereof.
U.S. Pat. No. 4,794,890, for example, discloses an Electromagnetic Valve Actuator. This patent teaches the use of a bi-stable electromechanical transducer to move the valves in an ICE. The patent teaches the need for some form of dampening at the end of either transition (open or closed) of the valves. Both mechanical springs and a fluid shock absorber as damper are disclosed as dampening means. While this invention controls ICE valve opening and duration, it has no provision for variable lift which is preferable to facilitate easy starting, idling and low speed operation. The dampening techniques proposed by this invention are also complex and raise reliability concerns.
U.S. Pat. No. 6,247,431 discloses an Electromagnetic Valve Actuating Apparatus for Internal Combustion Engine. This patent teaches the use of two solenoids formed on the ICE valve stem, one to open and one to close the valve. Additionally, springs on the valve hold the valve in a nominally closed position. The springs will serve to minimally cushion the opening of the valve and no other dampening or cushioning means is provided for valve closing. As a result, reliability of the disclosed system is suspect. Also, no provision is provided for variable lift adjustment of the valve.
U.S. Pat. No. 7,225,770 discloses an Electromagnetic Actuator Having Inherently Decelerating Actuation Between Limits. This patent attempts to solve the drawbacks of conventional valve actuation systems with yet another configuration of a solenoid system, albeit with coils, armatures and mechanical springs. The configuration and locations of the coils and armatures, the addition of ICE valve position sensing, and coil current control are an improvement over previous attempts to prevent valve destruction. However, reliability remains a concern and, again, no means are provided to adjust valve lift.
U.S. Pat. No. 5,983,847 and U.S. Pat. No. 6,293,303 each disclose the use of moving coils to actuate valves. However, the movement of the coil and its significant support structure and attachment hardware requires an undesirably large coil size and powerful electrical drive system. The corresponding mass, size, excessive drive forces needed, and complexity of the drive system makes such an arrangement impractical, unaffordable and unreliable for many applications such as modern ICEs.
Thus, there remains a need to provide a valve actuation system, method and device for ICEs that reduces cost, weight and complexity, while providing for independent control of a variety of valve actuation parameters.